1. Field of the Invention
The present invention relates to an electronic component package including an electronic component contained therein.
2. Description of Related Art
Various electronic components, such as semiconductor devices, quartz crystal oscillators and piezoelectric vibrators, are often contained in respective electronic component packages in order for the electronic components contained therein to be protected from an external environment.
As disclosed in Japanese Patent Laid-Open Publication Nos. 2000-58687 and 2000-164746, known electronic component packages include a case having a cavity that opens at the upper portion of the case for containing an electronic component, and a lid member fusion-welded to a peripheral edge surface of the case surrounding the opening located at the upper portion of the case, i.e. a case opening portion, with a soldering material in order to hermetically seal the cavity. The cavity defines an electronic component containing space which shuts out the external environment when the lid member is fusion-welded to the case so as to close the cavity.
As described above, the lid member has Ni layers formed of Ni and laminated on opposite sides of a core portion formed of a metal having a low expansion coefficient, such as Kovar. Various solder materials including, for example, Sn—Ag alloys, Bi—Ag alloys and In—Sn alloys are usable as the aforementioned soldering material.
The fusion welding of the lid member to the case is performed at a temperature equal to or higher than the melting point of the soldering material. Generally, heating is done at a temperature that is 20° C. to 30° C. higher than the melting point of the soldering material for a relatively short time, which may be as short as some tens of seconds, to minimize formation of a brittle intermetallic compound resulting from a reaction between the soldering material and an Ni-based metal.
An electronic component package containing an electronic component therein is fixed at a predetermined position on a circuit board by soldering, along with other electronic components. For volume production and the like, a method of soldering different components to a circuit board simultaneously is usually used, and the method includes the steps of positioning the components such as the electronic component package and other electronic components on the circuit board, and passing the whole circuit board through a heating furnace.
In this way, the electronic component package is previously heated for the fusion welding of the lid member to the case containing the electronic component via the soldering material, and then heated again for the soldering of the package to the circuit board. When the soldering temperature at which the electronic components are soldered to the circuit board is higher than the melting point of the soldering material used in the fusion-welding of the lid member, the fusion-welding portion between the case and the lid member is melted again to cause pinholes or cracks to be formed at the fusion-welding portion, so that the airtightness of the electric component containing space in the package is significantly decreased. If the airtightness of the electronic component package is to be maintained high, there arises a problem that the soldering temperature at which the package is soldered to the circuit board is limited to a low temperature, which is lower than the melting point of the soldering material used for the fusion welding of the lid member, so that soldering materials that can be selected for use in the soldering to the circuit board are also limited.